Southern Ocean deep-sea biodiversity: sampling strategies and predicting responses to climate change

The deep sea surrounds Antarctica and constitutes about 80%, of the Southern Ocean (SO) seabed. Scientific cruises (e.g. ANDEEP) reveal that SO abyssal life can be highly abundant, rich and endemic. With a vast water volume, the buffering effect of ice, data paucity and low sampling effort, signals of regional change may not be detected there for some time. The deep sea is likely to change in many ways, particularly becoming more acid and warmer, but over centuries or millennia. More immediate is the possibility of abrupt change in the thermohaline circulation driven by massive surface freshening from glacial melt-water. This could strongly stratify the water column, decrease ocean overturning and the flow of oxygen to the global deep sea. Impacts on abyssal biota will be hard to detect because we know so little about it. The most important first step is to generate a baseline of abyssal biodiversity and key factors generating and maintaining it. Recent work has shown abundance of a model taxon varied similarly in samples 1000s, 100s and 10s of kilometres apart. Most taxa were extremely patchy, and new sampling is needed to reveal patch size, spacing and importantly what structures abyssal patches, We examined the 'big picture' where factors at scales of less than kilometres may drive variability. The understanding of these patterns should make estimates of deep-sea biodiversity meaningful and give a baseline indicating the scale, taxon and environmental feature to look at in order to detect the inevitable signal of climate change in this huge, remote environment.

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